In recent years, for the purpose of global environment conservation, to reduce the use of fossil fuel, a refrigerant compressor with a higher efficiency has been developed. One approach for achievement of the higher efficiency of the refrigerant compressor is, for example, to reduce a surface pressure applied to the sliding surface of a slide unit included in the refrigerant compressor, thereby realizing smooth sliding.
The slide unit included in the refrigerant compressor is composed of a plurality of slide members which are combined via their sliding surfaces. As the specific example of the slide unit, there are a combination of a main shaft section of a crankshaft and a bearing section, a combination of a piston and a bore, a combination of a thrust section and a thrust washer, a combination of a piston pin and a connecting rod, a combination of an eccentric shaft of the crankshaft and the connecting rod.
As a technique for realizing smooth sliding of the slide unit, for example, there is a sealed compressor disclosed in Patent Literature 1. This sealed compressor accommodates an electric motor and a compressor machine in a sealed case. One of slide members of a slide unit of the compressor machine is provided with a phosphate coating film such as a manganese phosphate based coating film. This phosphate coating film is an insoluble coating film comprising a porous crystalline body.
As schematically shown in FIG. 13, the slide unit includes a first slide member 31 and a second slide member 41. The sliding surface of the second slide member 41 is provided with an insoluble phosphate coating film 20 comprising a porous crystalline body. For example, in a case where the slide unit includes the bore and the piston, the bore is the first slide member 31 and the piston is the second slide member 41. Or, in a case where the slide unit includes the main shaft section of the crankshaft and the bearing section, the bearing section is the first slide member 31 and the main shaft section is the second slide member 41.
In the configuration in which one of the slide members is provided with the phosphate coating film 20, the metal surface of the first slide member 31 and the surface of the phosphate coating film 20 of the second slide member 41, as their sliding surfaces, contact each other even when these slide members comprise metal. This can effectively reduce a possibility of the contact between metal surfaces of the sliding surfaces. Since the phosphate coating film 20 has the porous crystalline body, the retention capability of lubricating oil between the sliding surfaces can be improved. As a result, smooth sliding of the slide unit can be realized.
Patent Literature 1 also discloses that the phosphate coating film 20 covers the processed surface of the sliding surface which is formed by machine processing, and thus a compatibility between the slide members of the slide unit in an initial state can be improved.
Firstly, how the phosphate coating film 20 can suppress the contact between the metal surfaces will be described. For example, in the case where the slide unit includes the bore and the piston, a spacing (clearance) between the bore and the piston is typically set very small to minimize a leakage loss. Depending on conditions such as the shapes and non-uniform accuracy of the bore and the piston, there may be a possibility that the sliding surface of the bore and the sliding surface of the piston partially contact each other. The partial contact tends to occur when the piston reaches a top dead center or a bottom dead center and a sliding velocity becomes zero. As shown in FIG. 13, in the configuration in which the sliding surface of the piston (second slide member 41) is provided with the phosphate coating film 20, the metal surface is not exposed, and therefore, it becomes possible to avoid the metal surface of the piston from directly contacting the metal surface of the bore.
Next, how the phosphate coating film 20 can improve the retention capability of the lubricating oil will be described. When an oil pump is activated according to the rotation of the crankshaft included in the compressor machine, the lubricating oil is fed to the slide units and lubricates them. In the case of the slide unit including the bore and the piston as described above, the phosphate coating film 20 formed on the surface of the piston (second slide member 41) can retain the lubricating oil, in the slide unit of FIG. 13. The retained lubricating oil contributes to smooth sliding between the bore and the piston, and serves to seal the bore and the piston.